1. Field of the Invention
The present invention relates generally to electronic monitoring of power presses and similar machinery, and in particular to a system for electronically monitoring the braking efficacy for each and every cycle of operation of the powered machine.
More specifically this invention relates to a multimode electronic brake monitor system wherein an absolute encoder is used to provide precise displacement information of key elements of the powered machinery (illustratively a power press) to digital circuitry which performs a number of precision braking-safety related measurements.
2. Description of the Prior Art
In the use of power driven machinery for repetitive production cycles wherein an operator must manually interact with each cycle of operation, an operator safety hazard is always present to some degree. Over the years, many devices and methods have been employed to enhance the safety of manually operated machines while maintaining a suitable level of machine productivity. With power presses, or the like, where an operator must position (or reposition) a workpiece under dies and subsequently initiate a press cycle, it is important that automatic braking action of the press be monitored constantly to assure that an initially established set of safe operating conditions are maintained for the duration of the production run. These considerations have given rise to devices of various types specifically directed to monitoring the conditions of machine brakes under dynamic conditions. Additionally, recent government safety standards which set forth very specific performance requirements for brake monitors have also given rise to devices exhibiting some improvements in the art.
However, as is well known in the power machinery community, braking systems must respond to a wide variety of operating conditions and even for a single specific type of machine with automatic brakes in good operating condition, a wide range of braking times are encountered. Thus, a "cold-brake" stopping time may be substantially different from a "hot-brake" stopping time, and a machine stop order initiated on a downstroke portion of a cycle may take substantially longer to complete than one given on an upstroke portion. The situation is further complicated by the variation in machine stopping times due to the various set-ups used on a given press, and for each weight die used in a press. Any brake monitor which does not include provisions for compensating for these, and other variables, is at least difficult to set up, and may not achieve the proper mix of productivity and safety in order to skirt the problems associated with having an insufficient range of compensation features. Therefore, a brake monitor for a power press must respond sensibly to a range of conditions, and to date a truly satisfactory device has not been available.
Illustrative examples of prior art devices are found in U.S. Pat. No. 4,021,647 to Meier, which discloses an electronic brake monitoring device for use with power presses; in U.S. Pat. No. 3,268,047 to Grygera et al; and in U.S. Pat. No. 3,633,718 to Aystetten et al.